Depth sounder digitizer

ABSTRACT

A water depth digitizer produces a digital readout from a depth sounder of the type which produces an acoustic ranging pulse and which includes a transducer producing a receive signal representing the return of a reflected acoustic ranging pulse. A digital counter is started in response to an acoustic ranging pulse and is stopped in response to the receive signal occurring after the selected ranging pulse. In order to prevent erroneous readings which occur because the reflected acoustic ranging pulse is not of sufficient amplitude to be detected, a circuit is provided to detect valid information. The digital counter is reset when a receive signal is not received before the next occurring acoustic ranging pulse.

United States Patent McAlpin Oct. 3, 1972 [54] DEPTH SOUNDER DIGITIZERPrimary Examiner-Richard A. Farley Attorney-William J. Scherback,Frederick E. Dumoulin, Arthur F. Zobal, Andrew L. Gaboriault and SidneyA. Johnson [57] ABSTRACT A water depth digitizer produces a digitalreadout from a depth sounder of the type which produces an acousticranging pulse and which includes a transducer producing a receive signalrepresenting the return of a reflected acoustic ranging pulse. A digitalcounter is started in response to an acoustic ranging pulse and isstopped in response to the receive signal occurring after the selectedranging pulse. In order to prevent erroneous readings which occurbecause the reflected acoustic ranging pulse is not of sufficientamplitude to be detected, a circuit is provided to detect validinformation. The digital counter is reset when a receive signal is notreceived before the next occurring acoustic ranging pulse.

5 Claims, 1 Drawing Figure 1 l lPPS EXTERNAL CLOCK "1 Tutsi/mu EXTERNALRESET SYNC DECODEQ 1NH1B1T 59 DEGODE 5a 1810 81040 TRANSMIT SELECT RESET22 6&

L ss

2m 2400 SELECTED TRANSMlT PPS Q COUNTER TRANSMIT 10 RECEIVE WHOMETERscHmTT TRANSMIT GATE TRANSMIT TRIGGER ss PULSE 6m 85 H/ 12 27 OJms 2sAATATT Q,

ECHO lms O.lms

RECEIVE R GATE S TIMER TIMER RESET PATENTED 0m 3 I97? 3 696, 326

N0 DECODE 9 INHIBIT 59 DECODE 58 1 8 10 8 10 40 1PPS 1" 25 m.

FF 24 mfi'smn E TRESET 1 r 22 COUNT [\f GATE F-F U 2400 SELECTED PPSTRANSMIT so 1e E E COUNTER TRANSMIT ig 532 PULSE TRANSMIT GATEFATHOMETER SCHMITT PULSE 6ms s5 28 29 FATHOMETER RECEIV ECH E 58 SS 0has OJms RECEIVE RECEIVE GATE DEPTH SOUNDER DIGITIZER BACKGROUND OF THEINVENTION This invention relates to a digitizer for a water sounder andmore particularly to a digitizer which discriminates between accurateand inaccurate water depth measurements.

Depth sounders which measure the time of return of acoustic rangingpulses have been successfully used to accurately measure water depth.Recently, there has been a trend toward automation in hydrographicsurvey and oceanography which requires the automatic readout of depthfrom the depth sounder. Digital Readout Echo Sounder, by C. H. Cook,Proceedings of the IERE Conference on Electronic Engineering andOceanography, 1966, describes a system for automatic readout of depthfrom an echo sounder. U.S. Pats. Nos. 3,307,143 Wyse et al and 3,344,421Dildy, Jr., describes digital readout systems for echo ranging devices.

In some circumstances, a digitizer which produces a readout averagedover a plurality of depth soundings is required. Such a digitizer isdescribed in my copending application Ser. No. 862,204, field Sept. 30,I969, entitled Depth Sounder DIGITIZER. The operation of that depthsounder is quite satisfactory. However, in certain areas the reflectedacoustic ranging pulse is often quite weak and below the level ofdetection. When the reflected pulse is not received, the digitizerproduces an erroneous output. That digitizer includes a counter which isstarted by the acoustic ranging pulse and stopped by a receive signal.If the reflected pulse is not detected to produce this receive signal,the digital counter continues counting until the occurrence of the nextacoustic ranging pulse. This produces erroneous readings. The presentinvention is an improvement on the depth sounder digitizer of my pendingapplication.

SUMMARY OF THE INVENTION The water depth digitizer of the presentinvention discriminates between accurate and inaccurate water depthmeasurements. An accurate measurement of water depth is produced, or areading of zero is produced by the digitizer to indicate no measurementwas made.

The counter which accumulates counts representing water depth has areset circuit for returning the counter to zero when an inaccuratesequence of acoustic ranging and receive pulses occurs. The resetcircuit is enabled when a receive signal is not received before the nextoccuring acoustic ranging pulse. In one particular embodiment of theinvention a logic circuit is provided which accepts only a specifiedsequence of acoustic ranging and receive pulses within a given timewindow and rejects all other sequences. If an acoustic ranging pulse isfollowed by a receive signal within the given time period, an accuratewater depth readout is produced. If that sequence does not occur becauseof no reception of the reflected acoustic ranging pulse from the seabottom, or if the receive signal is not strong enough to trigger thegating circuitry in the depth sounder digitizer, water depth readout ofzero is produced.

In one particular embodiment of the invention the logic circuit includesa toggle flip-flop of the type having two steering inputs an a toggleinput. The accoustic ranging pulses applied to the toggle input. A countgate flip-flop is set by an acoustic ranging pulse and reset by thereceive signal. The output of the count gate flipflop is connected to asteering input of the toggle flipflop so that the next occurringacoustic ranging pulse will switch the state of the toggle flip-floponly if the count flip-flop is in the set position. The output of thetoggle flip-flop is connected to the reset circuit so that the counteris reset when the toggle flip-flop is switched.

The foregoing and other objects, features, and advantages of thisinvention will be better understood from the following more detaileddescription and appended claims in conjunction with the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a logic diagram of theinvention.

DESCRIPTION OF A PARTICULAR EMBODIMENT Referring to FIG. 1, the digitalcounter 10 produces a digitized readout representing water depth. Thecounter 10 is started in response to an acoustic ranging pulse appliedto the Schmidt trigger 11 and is stopped by the receive signal appliedto the single shot multivibrator 12. A reset circuit 13 resets thecounter 10 when an invalid combination of acoustic ranging and receivepulses occurs. The logic circuit for enabling this reset circuitincludes a toggle flip-flop 14 of the type having two steering inputsand a toggle input. As is standard in these type of flip-flops, themiddle input is a toggle input which can change the state of theflip-flop depending upon the condition of the other two inputs. Forexample, only when a l appears at the top input to the flip-flop willthe flip-flop be switched from the zero to the 1 state by the toggleinput.

A count gate flip-flop 15 is set by an acoustic ranging pulse and resetby the receive signal. The output of the count gate flip-flop 15 isconnected to the top steering input of toggle flip-flop 14. The acousticranging pulses are applied to the toggle input of flip-flop 14 so thatan acoustic ranging pulse will switch the state of the toggle flip-flop14 only if the count flip-flop 15 is in the set position. The output ofthe toggle flip-flop 14 is connected to the reset circuit 13 forresetting the counte 10 only when the toggle flip-flop is switched.

The remaining circuitry of the digitizer will be described beforedescribing in more detail the operation of the circuit.

This digitizer is of the same type described in my copending applicationin that water depth measurements are made only from selected acousticranging pulses. The depth sounder itself has a timing cycle which isasynchronous with respect to the equipment which receives and recordsthe digitized depth measurements. This equipment operates on its ownexternal clock and the digitizer of FIG. 1 is synchronized with thisexternal clock. In general there are many more depth sounder pulses thanare required to obtain the desired measurements. Therefore, only certaindepth sounder pulses are selected for measurement. In the particularembodiment being described one digitized depth sounder reading isobtained each minute.

The divide by 60 counter 16 establishes time synchronization between thedigitizer and the associated data recording equipment. This insures thata depth sounder reading is digitized and ready to be recorded for eachcycle of the recording equipment. The divide by 60 counter counts onepulse per second pulses from the external clock. The counter is reset bythe one pulse per minute clock.

Decoder 17 decodes the count of 9 from the counter 16 and sets the latchcircuit 18in response to the count of 9. The output of latch circuit 18enables gate 19 which sets the transmit select latch 20. This causes thereset circuit 13 to reset the counter 10.

The next occurring acoustic ranging pulse resets the transmit selectlatch 20. This triggers the single shot multivibrator 21. One outputfrom single shot multivibrator 21 is inverted by gating circuit 22 andsets the count gate flip-flop 15 to enable gate 16. This allows thedigital counter to start counting the 2400 pulse per second pulses.

A second output from single shot multivibrator 21 resets the toggleflip-flop 14 so that the upper output is a logic zero and the loweroutput is a logic 1. The output of count gate flip-flop 15, which is alogic 1 after being set by the selected acoustic ranging pulse, isapplied to the top steering input of the toggle flip-flop 14. This setsup the proper requirements for the toggle flipflop 14 to flip to theopposite state if a second acoustic ranging pulse occurs without areceive pulse in between. Note that all acoustic ranging pulses areapplied to the toggle input of the toggle flip-flop 14 through the gate23.

Assume that the receive signal from the selected acoustic ranging pulseis too weak to be detected. Then, the next pulse which occurs will bethe acoustic ranging pulse from the following depth sounding cycle. Thisacoustic ranging pulse will be applied through gate 23 to switch toggleflip-flop 14 so that the upper output is a logic 1 and the lower outputis a logic 0. The upper output of toggle flip-flop l4 acts through resetcircuit 13 to reset the counter 10 to zero. The lower output of toggleflip-flop l4 disables gate 16 to stop the 2400 pulse per second input tothe counter 10.

The upper output of toggle flip-flop l4 enables gate 24 to transmit theone pulse per second train to gate 19. This sets the transmit selectlatch circuit 20 in preparation for digitizing the next depth soundingcycle. The next acoustic ranging pulse resets the transmit select latch20 which triggers single shot 21. Single shot 21 produces the selectedtransmit pulse. This resets toggle flip-flop l4 and sets count gateflip-flop 15 to start a new count of the depth digitizing counter 10.

Now assume that the reflected acoustic ranging pulse is of sufficientamplitude to be detected. The receive pulse is transmitted throughsingle shot 12, single shot 27 receive gate 28, gate 29 and gate 30 toreset the count gate flip-flop 15. This disables gate 16 to stop thecounting of the counter 10.

The output of count gate flip-flop 15 is connected to the top steeringinput of toggle flip-flop 14. This is now a logic zero. This conditionprevents toggle flip-flop 14 from changing states when the toggle inputreceives a pulse. Therefore no further action takes place and thedigitized water depth is held in the counter 10 until the ninth secondof the next one minute period.

The receive gate timer is not shown in FIG. 1. This opens the gate 28 aselected time interval after the acoustic ranging pulse to furtherreduce error caused by spurious pulses. This is more fully explained inmy copending application.

While this invention can be implemented with many types of logiccircuit, the following components are examples of those suitable foruse:

Toggle Flip Flops: Motorola MC 853? NAND Gates: Motorola MC 846P While aparticular embodiment of the invention has been shown and describedmodifications are within the true spirit and scope of the invention. Theappended claims are intended to cover such modifications.

What is claimed is:

1. A water depth digitizer producing an averaged digital readout from adepth sounder producing acoustic ranging pulses in a plurality of depthsounding cycles and including a transducer producing receive signalsrepresenting the return of the reflected acoustic ranging pulsescomprising:

a source of clock pulses,

a digital counter driven by said source of clock pulses for producing adigitized readout averaged over said plurality of depth sounding cyclesand representing water depth,

means for starting said digital counter in response to the occurrence ofeach said acoustic ranging pulses,

means for stopping said digital counter in response to each of thereceive signals occurring after each acoustic ranging pulse so that saiddigital counter produces an accumulated count of said clock pulsesduring the time intervals between each of said acoustic ranging pulsesand their respective receive signals, said accumulated countrepresenting water depth averaged over said plurality of depth soundingcycles,

a reset circuit for said counter, and

means for detecting the sequence of occurrences of said acoustic rangingpulses and the respective reflected receive signals and for enablingsaid reset circuit when a receive signal produced by the reflection ofan acoustic ranging pulse is not received before the next occurringacoustic ranging pulse, the reset circuit setting said digital counterto zero to indicate that an inaccurate sequence of water depth soundingshas occurred.

2. A water depth digitizer producing a digital readout from a depthsounder producing acoustic ranging pulses and including a transducerproducing a receive signal representing the return of a reflectedacoustic ranging pulse comprising:

a digital counter producing a digitized readout representing waterdepth,

means for starting said digital counter in response to an acousticranging pulse,

means for stopping said counter in response to said receive signal sothat said digital counter accumulates counts representing water depth,

a reset circuit for said counter, and

means for enabling said reset circuit when a receive signal is notreceived before the next occurring acoustic ranging pulse, said meanscomprising:

a toggle flip-flop of the type having two steering inputs and a toggleinput, said acoustic ranging pulses being applied to said toggle input,

6 a count gate flip-flop which is set by an acoustic latch, and

ranging pulse and reset by said receive signal, means responsive to theresetting of said latch to the output of said count gate flip-flop beingconproduce aselected transmit pulse which is applied nected to asteering input of said toggle flip-flop so to Said means for StartingSaid counterthat the next occurring acoustic ranging pulse will 5 4. Thedigitizer recited in claim 3 wherein the output switch the state of saidtoggle flip-flop only if said of Said gg fl P- OP 18 Connected to setsaid transmit count flip-flop is in the set position, and Select latchwhen said toggle flip-flop 1s swltched m the output of said toggleflip-flop being connected to p p for dlgltlzmg the next depth Soundmg Y-said reset circuit for resetting said counter when Said toggk fli fl iSwitched 1O 5. The digitizer reclted in claim 3 wherein said 3. Thedigitizer recited in claim Zfurther comprising: Selected transmit PLllseis applied to reset said toggle a transmit select latch which isperiodically set, said acoustic ranging pulses being applied to resetsaid

1. A water depth digitizer producing an averaged digital readout from adepth sounder producing acoustic ranging pulses in a plurality of depthsounding cycles and includIng a transducer producing receive signalsrepresenting the return of the reflected acoustic ranging pulsescomprising: a source of clock pulses, a digital counter driven by saidsource of clock pulses for producing a digitized readout averaged oversaid plurality of depth sounding cycles and representing water depth,means for starting said digital counter in response to the occurrence ofeach said acoustic ranging pulses, means for stopping said digitalcounter in response to each of the receive signals occurring after eachacoustic ranging pulse so that said digital counter produces anaccumulated count of said clock pulses during the time intervals betweeneach of said acoustic ranging pulses and their respective receivesignals, said accumulated count representing water depth averaged oversaid plurality of depth sounding cycles, a reset circuit for saidcounter, and means for detecting the sequence of occurrences of saidacoustic ranging pulses and the respective reflected receive signals andfor enabling said reset circuit when a receive signal produced by thereflection of an acoustic ranging pulse is not received before the nextoccurring acoustic ranging pulse, the reset circuit setting said digitalcounter to zero to indicate that an inaccurate sequence of water depthsoundings has occurred.
 2. A water depth digitizer producing a digitalreadout from a depth sounder producing acoustic ranging pulses andincluding a transducer producing a receive signal representing thereturn of a reflected acoustic ranging pulse comprising: a digitalcounter producing a digitized readout representing water depth, meansfor starting said digital counter in response to an acoustic rangingpulse, means for stopping said counter in response to said receivesignal so that said digital counter accumulates counts representingwater depth, a reset circuit for said counter, and means for enablingsaid reset circuit when a receive signal is not received before the nextoccurring acoustic ranging pulse, said means comprising: a toggleflip-flop of the type having two steering inputs and a toggle input,said acoustic ranging pulses being applied to said toggle input, a countgate flip-flop which is set by an acoustic ranging pulse and reset bysaid receive signal, the output of said count gate flip-flop beingconnected to a steering input of said toggle flip-flop so that the nextoccurring acoustic ranging pulse will switch the state of said toggleflip-flop only if said count flip-flop is in the set position, and theoutput of said toggle flip-flop being connected to said reset circuitfor resetting said counter when said toggle flip-flop is switched. 3.The digitizer recited in claim 2 further comprising: a transmit selectlatch which is periodically set, said acoustic ranging pulses beingapplied to reset said latch, and means responsive to the resetting ofsaid latch to produce a selected transmit pulse which is applied to saidmeans for starting said counter.
 4. The digitizer recited in claim 3wherein the output of said toggle flip-flop is connected to set saidtransmit select latch when said toggle flip-flop is switched inpreparation for digitizing the next depth sounding cycle.
 5. Thedigitizer recited in claim 3 wherein said selected transmit pulse isapplied to reset said toggle flip-flop.